He calls himself a sonic archeologist. But instead of a pick and shovel, Steve Berkowitz uses his ears and a lifetime of musical knowledge to dig up gems from the past and safeguard them for the future.His latest dig is Through the Open Window, 1956-1963, the 18th chapter in the Bob Dylan Bootleg Series, chronicling the period when the young folksinger left his Minnesota home and headed to New York, with the siren call of Woody Guthrie in his head.Through The Open Window spans the period when